|Rugby World Cup Pool A: England v Wales|
|Venue: Twickenham Date: Saturday, 26 September Kick-off: 20:00 BST|
|Coverage: Live on BBC Radio 5 live, plus live coverage on the BBC Sport website.|
Saturday's World Cup clash between England and Wales is the game everyone wants to see. It will be monumental, a fabulous occasion. I can't wait.
Whichever team comes out on top at Twickenham will give themselves a massive advantage in reaching the knock-out stages.
England can still qualify even if they lose on Saturday, but they then have to beat Australia, so it becomes much harder.
Given Wales' record against Australia (the Welsh have lost their last 10 meetings), the dark side of defeat is bigger for Wales, whereas there is still light at the end of the tunnel for England.
'England selection puts Lancaster's job on line'
The build-up has been dominated by England's decision to drop George Ford for Owen Farrell at fly-half and bring in former rugby league international Sam Burgess at inside centre.
They are two selections that could be the difference between winning and losing - and the difference between Stuart Lancaster keeping his job as head coach or not.
Head coaches of Tier 1 nations keep their jobs based on results, and results are based on them making the right selections.
Lancaster has made a huge decision at 10. In essence, he is telling Ford "we feel Owen Farrell is a better goal-kicker than you, and a stronger defender" because, in everything else, Ford has a greater skill-set.
So all Farrell has to do is defend really well and kick his goals, and that selection will be justified. But I'd expect Owen to do a great job doing what he's been asked to do. He has a head to handle most situations and won't be fazed by the magnitude of Saturday's game at all.
'Wales centre pair have the edge '
In Jonathan Joseph's absence through injury, Lancaster has chosen the 'double-barrelled' option of Burgess and Barritt, without a playmaker. We won't know whether it is the right or wrong decision until after Saturday's game, but the coach has gone with England's DNA, which is route one.
A midfield of Farrell, Burgess and Barritt looks powerful, and any finesse will have to come from outside with Jonny May and Anthony Watson on the wings.
Burgess has to barrel over the gain-line and be stronger and more powerful than Wales centre Jamie Roberts.
But as a pairing, Roberts and Scott Williams have the edge. The combination of skill-sets is better than England have in Burgess and Barritt, who have never played together before.
Roberts picks some great lines, as you would expect of someone with 70 Wales caps and three Lions Tests behind him.
Williams is someone I would have picked out as a potential player of the tournament. He has a great step, good acceleration and is a beefy boy.
Never mind the backs, what about the frontline?
But what happens in the backline is going to be almost irrelevant compared with what happens up front. You can't look past this match-within-a-match.
Which pack can get it together enough to deal with the pressure and expectation and responsibility this match brings?
It will be a battle of wills, power and mental strength. Each forward must have the attitude of "I am going to impose myself on you and win our one-on-one battle - face to face, chest to chest, body to body", without losing sight of the bigger picture that they are part of a team.
England have been able to do that on certain occasions under Lancaster - when they beat the All Blacks in late 2012, when they beat Australia in the last two autumn campaigns - but they have been found wanting at other times, notably in Six Nations-deciding games.
This is such a big confrontation of minds, bodies and will, and the English forwards have to win the confrontation.
'England scrum must man up'
Warren Gatland is a more experienced coach and he has made some big selection decisions in his time. He has gone big by picking Tomas Francis at tight-head prop. He knows that is a perceived weakness for England, and if they don't shore it up, Francis could destroy them there.
Gatland will believe Francis can do a number on England's loose-head prop Joe Marler, who can get on the wrong side of referees and tends to shift inwards at scrums. If that happens England will be under the pump and Wales fly-half Dan Biggar will punish them with penalties.
If England's front five 'man up', England will win at home. If they don't, their back row will be ineffectual and won't give half-backs Ben Youngs and Farrell the platform of quick ball they need.
England's front five have not done that consistently in the last few matches; they looked leaden-footed in Paris, were OK for 30 minutes against Ireland, and were all over the place for 60 minutes against Fiji. Their scrum has been way below par of late - I never thought I would see a Fiji scrum put away an England pack, even once.
Lancaster could have made changes, but he has picked them again because they owe him, and they owe themselves. They won't be there next time if they don't step up. My sense is they will.
'Experience counts in big games'
Over the past 10 matches between the countries it may be all-square but this match is at Twickenham, where England haven't lost to a northern hemisphere team since 2012 (a run of 11 matches).
No matter what Gatland is saying about his record there (Wales have won two of their five matches at Twickenham under his charge), those wins were both during Grand Slam campaigns and by no more than seven points. It is not the poorest record, but it is not the greatest either.
|England v Wales - past 10 meetings|
|Feb 2015: Wales 16-21 England||Mar 2014: England 29-18 Wales|
|Mar 2013: Wales 30-3 England||Feb 2012: England 12-19 Wales|
|Aug 2011: Wales 19-9 England||Aug 2011: England 23-19 Wales|
|Feb 2011: Wales 19-26 England||Feb 2010: England 30-17 Wales|
|Feb 2009: Wales 23-15 England||Feb 2008: England 19-26 Wales|
What Wales do have in their favour is more experienced players across the board - Gethin Jenkins and Alun Wyn Jones in the front five, their whole back row, Roberts and George North in the backs.
These guys are British and Irish Lions, and they have played in a World Cup semi-final, which is bigger than this game for the individual.
They have masses of experience compared with their opposite numbers, and that is of huge benefit. You are much more relaxed having been through big games like this before.
So who will prevail?
I predict both teams will get through the group. The psychology is a big barrier for Wales in their final game against Australia, but I think being away from home at Twickenham, where they play regularly, will help them.
This World Cup has already been sparked into life by Japan, Argentina, Georgia and the other smaller nations. They have been inspiring.
Now England need to be inspired, and inspire a nation themselves.
My sense is they will front up, and win by a single score. It will be very close, but they will do the job - just.
Jeremy Guscott was speaking to BBC Sport's Bryn Palmer.
|More from BBC Sport|
|What England v Wales means to us|
|Smash Burgess and the rest - Gatland|
|Warburton relishes 'biggest game'|
|Lancaster accepts increased scrutiny|
|For the latest rugby union news, follow @bbcrugbyunion on Twitter|